During resolution, it has to still be in the process of attacking. How is it going to be destroyed if it is not in the process of attacking? Magic Cylinder, Negate Attack, Draining Shield, etc are examples why this is true. Mirror Force represents this as well. How is the attacking monster going to be destroyed if he somehow gets to Defense Position and not Attack Position? This is a card that has a specific timing and a specific resolution that has to occur in order for it to work.